This section is intended to provide information relevant to understanding various technologies described herein. As the section's title implies, this is a discussion of related art that should in no way imply that it is prior art. Generally, related art may or may not be considered prior art. It should therefore be understood that any statement in this section should be read in this light, and not as any admission of prior art.
Generally, energy harvesting from an ambient environment is an integral factor for self-sustaining sensor nodes, and as such, harvesting minuscule levels of input power sources may enable new application fields. For instance, a miniature 100×100 μm solar cell may generate ˜150 pW under low lighting conditions (e.g., 32 lux). In this instance, efficient DC-DC up-conversion from such a low power source voltage to a typical higher power battery voltage may be difficult. In some cases, conventional DC-DC converters may be used in various techniques to reduce input power for harvesting. However, these conventional harvesting techniques are typically bounded by continuous charge pump leakage, which reduces efficiency and overall performance of energy harvesting.
FIG. 1 illustrates a block diagram of a conventional continuous harvester 100 as known in the art. As shown, this harvester 100 may include a continuous charge pump 140 coupled between a solar cell (SOL) and a battery (BAT). In some cases, this charge pump 140 may be implemented as some type of DC-DC converter (e.g., either inductor based or switched-capacitor based DC-DC converters) that may use energy storage elements to generate a continuous power source. Some design techniques have attempted to reduce clock power or quiescent power to extend harvesting power range. However, as with other conventional techniques, these design techniques are typically bounded by continuous charge pump leakage, which may reduce efficiency and overall performance of energy harvesting. Further, in conventional energy harvesting, harvester loss is drawn from maximum power point tracking (MPPT) loss and charge pump efficiency loss. As such, although conventional continuous harvesting may have high solar efficiency, overall efficiency is typically bounded by constantly low efficiency of DC-DC conversion at ultra-low input power levels.